All files where an identifiable human face is present require a model release. There are no exceptions. This includes illustrations based on photography or sketches of people as well as drawing from a real-life model. In some cases a release may be required even if the face us not identifiable. Please see the 'Contextual Model Releases' section of this article for a complete explanation.
If the photograph is of a minor (a child under the age of 18), a model release should be signed by a parent or legal guardian.
If the photo is of the photographer (a self portrait), a model release is still required.
A model release should be uploaded with each file. If you're uploading successive shots of the same model, the model release should be uploaded with each shot.
A valid witness signature must appear on the model release.
iStock does not accept digitally created or digitally signed model releases, (this includes using script fonts as a signatures, e-signatures and scanning signatures and then pasting into the model release).
The requirement for a property release isn't as clear-cut as for a model release, because there is no specific right of privacy that attaches to property, as it does to people. Having said that, there are at least two reasons for obtaining property releases: (i) on the theory that a person's identity might be connected to the property in question (such as where a person's property is used in a manner that might defame the person as owner); and (ii) on the basis that to use someone's property for commercial gain without their consent may amount to an offense called conversion. Also, if you go on someone's private property to take a picture of them or their property, it could amount to trespass.
iStock recommends that a Property Release be obtained when the image contains identifiable property wherever possible (this isn't just for houses, it could apply to pets, cars and other personal property. The more recognizable and unique the property (and the more the owner's identity might be connected to or determined from the property) the greater the need for a property release.
The Property Release needs to signed by the legal and beneficial owner(s) of the property or their authorized agent. Many of the same formalities apply as for Model Releases.